Isolation and Screening of ACC Deaminase-Producing Microbes for Drought Stress Management in Crops

The compound aminocylopropane-1-carboxylic acid (ACC) is the product of Yang cycle, which plays a vital role in drought response, salt stress, host-pathogen interactions, seed germination, flowering, and fruit ripening. While ACC is produced within the plant, some of it is exuded from the roots where it may alter the rhizosphere microbial composition. Within the plant, ACC may be converted to the phytohormone ethylene by the action of the plant enzyme ACC oxidase (ACO). When the rhizosphere or the plant endosphere contains microbes that produce ACC deaminase, some of the ACC is converted to alpha ketobutyric acid and ammonia. Thus, reducing ethylene production and decreasing the negative effects of ethylene including numerous drought-like symptoms, thereby reduces the deleterious effects of drought stress. ACC deaminase-producing microorganisms may readily be isolated by using minimal medium containing ACC as sole source of nitrogen and a pH indicator. The microbial cleavage of ACC changes the pH of the growth medium and causes an easily detectable color change around the colony. Subsequently, qualitative or quantitative assays for alpha ketoglutaric acid or ammonia may be used to assess the level of ACC deaminase activity.